This invention relates generally to water-based coating compositions and, more particularly, to water-based coating compositions which cure in at least two stages, an initial rapid cure stage in which a protective film is formed, and a slower curing stage in which a final hard coating with outstanding wear characteristics is produced. In addition, the coating compositions can be applied and will cure rapidly under a wide range of environmental conditions, are free of environmentally objectionable organic solvents such as glycols, glycol ethers, paint thinners, etc., and are outstandingly long-wearing and adherent.
In one important embodiment, this invention relates to water-based coatings which can be applied to asphalt and concrete road surfaces and other types of pavements under weather conditions ranging from sunshine to rain to cool temperatures, yet can be driven on almost immediately after application under all of these application conditions.
In another important embodiment, this invention relates to solvent-free rapidly curing coating compositions suitable for application to steel and other surfaces commonly coated with conventional epoxy systems. In yet another important embodiment, the invention relates to coatings which can be applied at substantial thicknesses without significant sagging even on vertical and underside surfaces. In a still further embodiment, this invention relates to new water-based asphalt emulsion coating compositions which can be applied to roads, tarmacs, driveways and other surfaces by spraying, which dry almost instantaneously and which resist gasoline and most organic solvents.
Although the present invention will find application in numerous areas from traffic paints, to coatings for steel and other materials, to asphalt emulsions, for convenience, the primary focus of the description below will be on traffic paint applications. The invention, however, is not intended to be so limited but rather is to be construed as having application in any environment to which it is suited.
Traffic paints are the most common asphalt and concrete road coatings. For decades, traffic paints have been formulations of alkyd combined with various resins. Such formulations usually contain environmentally objectionable organic solvents. They cure or dry slowly, and therefore present logistical problems in preventing road traffic from destroying or degrading the markings before the paint is dry. Finally, alkyd/resin coatings lose thickness due to loss of solvent on drying and are not as durable as might be desired, particularly in demanding traffic applications.
In recent years, more durable coatings have been developed for traffic applications. These include epoxy and polyester paints, preformed tapes and thermoplastics.
Epoxy paints have the greatest potential as traffic paints in terms of durability and cost-effectiveness. Yet, in application, epoxy paints have heretofore presented serious drawbacks. Conventional epoxy paints use a two component epoxy mixed with a solvent which keeps the mixture fluid until it is ready to be applied. The presence of the solvent is environmentally highly undesirable, since it is ultimately released into the atmosphere. In addition, conventional epoxy coatings lose thickness on drying and tend to yellow with the passage of time.
Recently introduced epoxy paints having 100% solids eliminate the solvent release problem, but have other significant drawbacks. For example, 100% solids systems require heating before application, which makes them more difficult and expensive to use. In addition, since these systems typically require two parts of a highly viscous epoxy resin to one part curing agent, the mixture is mechanically difficult to use. These 100% solvent-free epoxy paints require about 15 minutes to cure to a degree sufficient to permit drive-over in traffic paint applications. Thus, the logistical problems of traffic re-routing are still present for both the conventional solvent-based and the solvent-free epoxy coatings since both require time to dry before traffic can pass over them.